Monochromatic or color liquid crystal display panels have been recently paid much attention as flat displays. The liquid crystal display panels include those of active matrix system and those of simple matrix system. In the color liquid crystal display panels of both systems, a color filter is used. For example, a color liquid crystal display panel of active matrix system using a thin film transistor (TFT) is formed by placing a TFT substrate and a color filter to face each other and sealing a liquid crystal layer between a substrate of the TFT substrate and a substrate of the color filter. For the color filter, three primaries of red (R), green (G) and blue (B) are used, and the liquid crystal acts as a shutter by switching on or off an electrode corresponding to each pixel of R, G and B, whereby transmission of each light of the three primaries is controlled to effect color display. On the other hand, the TFT substrate comprises a transparent substrate, a semiconductor device and a pixel electrode, said semiconductor device and said pixel electrode being formed integrally with each other on the transparent substrate. The semiconductor device is a thin film transistor (TFT) composed of a gate electrode, a gate insulating layer, a semiconductor layer made of amorphous silicon (a-Si) or the like, a source electrode and a drain electrode. One end of the drain electrode is connected with the semiconductor layer, and the other end thereof is connected with the pixel electrode. Further, an alignment film is formed to cover the semiconductor device and the pixel electrode.
In the semiconductor layer made of a-Si or the like, however, an photocurrent is large, and therefor the semiconductor device is required to be shielded from light to inhibit leaking of the photocurrent. Accordingly, the color filter is constructed by forming a light-shielding layer (black matrix), colored layers of R, G and B, a overcoat, a transparent electrode layer and an orientation layer on a transparent substrate. The light-shielding layer also serves to enhance chromaticness and display contrast in addition to the inhibition of leaking of the photocurrent. Such a light-shielding layer as mentioned above is required to be provided not only in the color liquid crystal display panels but also in the monochromatic liquid crystal display panels for the same reason.
As the light-shielding layer, there have been conventionally known a light-shielding layer obtained by forming a relief through photoetching of a chromium thin film, a light-shielding layer obtained by dyeing a hydrophilic resin relief, a light-shielding layer obtained by forming a relief using a photosensitive resin in which a black pigment is dispersed (see: Japanese Patent Laid-Open Publications No. 1(1989)-102429, No. 1(1989)-239523 and No. 2(1990)-239204), a light-shielding layer obtained by electrodeposition of a black electrodeposition paint, a light-shielding layer obtained by metal-plating with a given pattern on a cured polymer film containing a catalyst for electroless plating to form a metallic thin film (see: Japanese Patent Laid-Open Publication No. 2(1990)-251801), and a light-shielding layer obtained by printing.
However, there are various problems in those conventional light-shielding layers. For example, the light-shielding layer obtained by forming a relief through photoetching of a chromium thin film needs a vacuum process such as deposition or sputtering in its preparation, or the process for preparing the light-shielding layer is complicated, resulting in high production cost, though the layer shows high dimensional accuracy. Further, in this light-shielding layer, a reflectance of chromium is necessarily restrained to enhance the display contrast under an intense external light, and therefore it is necessary to further conduct sputtering of chromium having a low reflectance, resulting in much higher production cost. The light-shielding layer obtained by using a photosensitive resin in which a black dye or a black pigment is dispersed, though the production cost of this layer is low, has such problems that a photo process becomes unstable and satisfactory light-shielding properties can be hardly obtained because the photosensitive resin is black, whereby black matrix of high quality cannot be obtained. The light-shielding layer obtained by forming a metallic thin film through electroless plating has a problem of high reflectance because metal is deposited only on a surface of the curable film.
By the way, in the process for preparing a liquid crystal display panel, the light-shielding layer is required to be formed with extremely high accuracy from the viewpoint of alignment of the light-shielding layer and the semiconductor device on the TFT substrate, and this alignment operation is also required to be made with high accuracy. Therefore, yields of the liquid crystal display panels are compelled to be reduced in the conventional process. For shielding the semiconductor device from light much more effectively, a method of enlarging a width of the light-shielding layer can be mentioned. However, this method still has a problem. That is, if the width of the light-shielding layer is enlarged, an aperture ratio of the resulting liquid crystal display panel becomes small, and thereby brightness of the panel is reduced.
To solve the above-mentioned problems, a method of forming a light-shielding layer directly on the semiconductor device of the TFT substrate is carried out (see: Japanese Patent Laid-Open Publication No. 60(2985)-184228). Even by the use of this method, however, there has not been obtained yet a liquid crystal display panel having a light-shielding layer which shows a high optical density, a low reflectance and a high dimensional accuracy and which can be easily prepared without using a vacuum process.
It is an object of the present invention to provide a black matrix substrate employable for a flat display such as a liquid crystal display panel, an imager such as CCD or a color filter of such as a color sensor and showing a high dimensional accuracy, excellent light-shielding properties and a low reflectance, and a process by which such a black matrix substrate as mentioned above can be prepared at a low cost.
It is another object of the invention to provide a color or monochromatic liquid crystal display panel in which display can be effected with high precision and high contrast and which can be easily prepared, and a process for preparing such a color or monochromatic liquid crystal display panel as mentioned above.